With the dramatic increase in oil prices earlier this year translating into higher prices at the gas pump in the United States, concerns over U.S. dependence on foreign oil are once again part of the national discussion on energy security. Combined with the growing understanding that carbon emissions from the combustion of fossil fuels are driving global climate change, the debate is now focused on how to restructure the U.S. transport system to solve these two problems. While the idea of running U.S. vehicles on natural gas has lately received a great deal of attention, powering our cars with green electricity is a more sensible option on all fronts—national security, efficiency, climate stabilization, and economics.

Having a fleet of natural gas–powered vehicles (NGVs) would simply replace U.S. dependence on foreign oil with a dependence on natural gas, another fossil fuel. The United States has scarcely 3 percent of the world’s proved natural gas reserves, yet even without the increased demand that would result from an NGV fleet, the country already consumes nearly a quarter of the world’s natural gas. At current rates of consumption, U.S. proved reserves would only meet national demand for another nine years.

U.S. natural gas production has remained relatively constant over the last two decades and is unlikely to increase over the long run, despite growing consumption. Consequently, any rise in demand is likely to be met by increasing imports. Since the late 1980s, U.S. net imports of natural gas—primarily from Canada—have tripled. The U.S. Department of Energy projects that by 2016 the majority of U.S. natural gas imports will come from outside North America.

With Russia and Iran topping the list of countries with the largest proved reserves of natural gas, a growing reliance on imports would increase the strategic vulnerability of the United States. These two nations—which along with 14 others collectively control nearly three fourths of the world’s natural gas reserves—are members of a Gas Exporting Countries Forum that was established in 2001. While there is no direct evidence that these countries are seeking to form a natural gas cartel, at the Forum’s 2005 annual meeting they discussed how to maintain a satisfactorily high natural gas price. (See data).

Just like oil, natural gas is a finite, nonrenewable resource. This means that switching to a fleet of NGVs would be at best a short-term fix. As natural gas becomes more difficult to obtain and more costly, a fleet of NGVs and the 20,000 or so natural gas refueling stations that would be required to support them would simply be abandoned.

A better investment is one that supports a fleet of plug-in hybrid electric vehicles (PHEVs), such as the Chevy Volt slated for sale in 2010, which can use the existing electric infrastructure. A study by the U.S. Department of Energy’s Pacific Northwest National Laboratory found that if all U.S. automobiles were PHEVs, the current U.S. infrastructure could provide power for more than 70 percent of the fleet. Battery charging would occur mostly at night, when demand for electricity is low. In the emerging energy economy—an economy built on domestic wind, solar, and geothermal energy sources—the greening of the grid by replacing fossil fuel–based electrical generation will also be a greening of the transport system. Beyond the grid, distributed power systems—solar cells on rooftops, for example—could also be used to power PHEVs.

With today’s energy mix, PHEVs running on electricity from the grid are nearly three times more efficient than NGVs on a “well-to-wheel” basis—that is, when considering the full life cycle of the energy source, from fuel extraction to combustion to vehicle propulsion. This is because internal combustion engines, such as those used in natural gas vehicles and in today’s gas-powered automobile fleet, are incredibly inefficient. Only 20 percent or so of the energy in the fuel is used to move the vehicle. The other 80 percent is wasted as heat. Thus, choosing electric vehicles over NGVs can sharply reduce energy demand.

This important fact seems to have escaped T. Boone Pickens, the legendary oil tycoon from Texas who is now promoting a plan to replace natural gas in the electric power sector with wind-generated electricity and use the freed up natural gas to power a fleet of NGVs. Burning natural gas in a new combined cycle power plant is three times as efficient as burning natural gas in a car. Even including electrical losses from transmission, distribution, and battery charging, running a car on electricity from a natural gas power plant is more than twice as efficient. Keeping natural gas in the electric sector to help power a fleet of PHEVs is therefore the logical choice. Wind-generated electricity should replace electricity from coal-fired power plants, the most polluting power source.

Under normal driving conditions, well-to-wheel carbon dioxide emissions for vehicles running on electricity from natural gas–fired power plants are one fourth as high as emissions from cars directly burning natural gas. Since a PHEV operating in electric-only mode has no tailpipe emissions, electrifying transport would move the majority of carbon emissions from millions of vehicles to centralized electricity-generating plants, greatly simplifying the task of controlling emissions. As fossil-based power generation is replaced with wind and solar power, cumulative carbon emissions from centralized power facilities will be greatly reduced.

Carbon pollution is not the only environmental concern. Over the last decade, the decline in U.S. conventional natural gas production has been offset by turning to more unconventional sources, such as coalbed methane, tight sandstones, and gas shales. Between 1998 and 2007, this unconventional production increased from 28 to 47 percent of total output. Growing reliance on gas shales in particular is raising concerns about water consumption and contamination. Extracting gas from this source involves hydraulic fracturing, a process that injects water, sand, and chemicals into the shale layer at extremely high pressures. The process can use millions of gallons of water per extraction well and is known to leak chemicals into surrounding aquifers. The Commissioner of the Department of Environmental Protection for New York City recently wrote to the New York State Department of Environmental Conservation voicing concerns that drilling for natural gas in the Marcellus Shale formation will contaminate New York City’s watershed, jeopardizing drinking water. Opposition to unconventional production is likely to rise as gas companies attempt to expand operations into increasingly sensitive areas.

On economics, driving with electricity is far cheaper than driving with gasoline or natural gas. The average new U.S. car can travel roughly 30 miles on a gallon of gasoline, which cost $3.91 in July 2008 (the latest date for which comparable price data for natural gas is available). Traveling the same distance with natural gas cost around $2.51, while with electricity, using the existing electrical generation mix, it cost around 73¢.

In addition to being cheaper, electricity is less vulnerable to price shocks than natural gas. Electricity is generated from many different energy sources, so the impact of a quick rise in the price of any one fuel is usually tempered by stable prices for other fuels. In the new renewable energy economy, electricity prices will be insulated against fuel shocks, since energy from the wind and the sun is abundant and free.

While the price of residential electricity in the United States has increased only 30 percent since 1995, the price of natural gas has more than tripled due to rising demand and production costs. With the fast-industrializing economies of China and India expected to compete with the United States for natural gas, prices will likely continue their sharp upward trend.

Choosing natural gas to power our vehicles would send the United States down the same expensive and inefficient path that created our addiction to foreign oil and our dependence on a resource that will ultimately run out. Choosing green electricity can take us in a new direction—one that leads to improved energy security and a stabilizing climate.